1. Field of the Invention
The present invention relates to a piston ring engaged with a piston ring groove of a piston of an internal combustion engine or the like.
2. Description of the Related Art
Piston rings are broadly classified into oil rings and pressure rings. In any case, a piston ring may comprise a piston ring main body, and an expander, arranged on the inner peripheral surface side of the piston ring main body, for imparting a pressing force in the diameter expanding direction of the piston ring main body.
In such a piston ring, the sum of the piston ring main body and the pressing force of the expander forms the tension of the piston ring as a whole. This tension of the piston ring as a whole is set so that the piston ring can display the functions thereof even under the severest conditions permitting use of the piston ring. For example, in a piston ring installed in a piston of an internal combustion engine, a piston ring tension is set on the assumption of a high speed-high load state of the internal combustion engine.
In a piston ring comprising a piston ring main body and an expander, therefore, a pressing force of the expander is of course set on the assumption of the high load condition of the internal combustion engine or the like.
In a conventional piston ring, however, engine oil adhering to the inner peripheral surface of the cylinder has an increasingly larger force causing the piston ring to float up under the effect of the oil hydraulic pressure generated between the cylinder inner peripheral surface and the piston ring along with the increase in the speed of reciprocation of the piston. The oil consumption tends to become larger according as the speed and the load become higher. Therefore, the tension of the entire piston ring is set on the assumption of a high speed and high load state, i.e., a high temperature state of the internal combustion engine. In a low speed and low load state, i.e., a low temperature state of the internal combustion engine, a tension higher than the necessary level would act on the inner peripheral surface of the cylinder, thus resulting in friction. In this case, it is also conceivable that a tension for the entire piston ring is set on the assumption of a low speed and low load state. In this state, however, the high speed and high load operation is not desirable because it causes a sudden increase in the coil consumption.
Apart from the above-mentioned problems, the following problem has been encountered.
In other words, when attaching a conventional piston ring comprising a piston ring main body and an expander to a piston, it was necessary to follow the procedure shown in FIG. 4. With reference to FIG. 4, a piston ring comprising a two piece combined oil ring 50 composed of an oil ring main body 51 and a coil expander 52 will be described.    (1) Disengaging a connecting section 54 of the coil expander 52 (see FIG. 4(a));    (2) Winding the coil expander 52 around an oil ring groove 55, and connecting the connecting section 54 with a connecting pin 56 (see FIG. 4(b)); and    (3) Attaching the oil ring main body 51 to the oil ring groove 55 so that an engaging port 511 is at a position at 180 relative to the position of the coil expander 52 (see FIG. 4(c)).
According to this attaching method, it is necessary to once disengage the connecting section of the coil expander and connect the connecting section again. This is troublesome, and in addition, this operation cannot be automated, resulting in the necessity to manually conduct all steps of operation.
The present invention was developed to solve these problems, and has a main object to provide a piston ring which generates tension suitable for the low speed and low load state and the high speed and high load state, respectively, and solve troublesome work of attaching a piston ring comprising a piston ring main body and an expander in a piston ring groove of a piston of an internal combustion engine or the like.